The present invention relates generally to compositions and methods for the treatment of substrates, and more particularly relates to compositions and methods for treating substrates to enhance the quality of images printed thereon. The invention is useful in the treatment of a wide variety of substrate types, including flexible and rigid substrates, porous and nonporous substrates, cellulosic and noncellulosic substrates, and the like.
As printing technology advances, manufacturers of many different types of products are faced with the increasingly rigorous demands of their customers for high quality printed images on those products. Such products include, for example, printed textiles, paper, printed polymeric sheets, coatings or films, printed metallic items, and the like.
For example, current textile printing technologies are deficient in meeting modern, time-driven, demand-responsive manufacturing strategies. In general, the conventional method of printing on textiles involves crosslinking a colorant to the cellulosic fiber of the textile itself. This approach is limited in that it relies on processes that involve multiple, time-consuming steps. The types of substrates and colorants that can be used are limited as well. One approach for increasing textile printing speed involves the use of inkjet printing. Inkjet printers are very popular, due at least in part to their reliability, relatively quiet operation, versatility, graphics capability, print quality, and low cost. Moreover, inkjet printers have made possible xe2x80x9con demandxe2x80x9d color printing without the need for complicated devices. Because inkjet printing has become so popular in both home and commercial use, several water-soluble inks are available. The inks are typically composed of water and a colorant, usually a dye or pigment dispersion, and often contain a number of additives for imparting certain features to the ink (e.g., improved stability and flow, smear resistance, and the like). Unfortunately, however, using inkjet printing techniques for printing on textiles has met with several problems. First, and in spite of the large number of inkjet inks currently available, inkjet printed images on textiles are often of low quality. For example, the printed images often smear upon handling, exhibit bleed (the intrusion of one color into an adjacent color), are moisture sensitive, and are dull, i.e., colored inks when printed fail to accurately produce the expected hues. Moreover, the printed images are often neither water-fast nor detergent-resistant, resulting in fading of the printed image after washing. Printed textile images with these drawbacks are wholly unacceptable to the textile industry, which requires not only that the image be both water-resistant and detergent-resistant, but also that the colors and hues are those deemed acceptable in the textile field.
In addition, there is a keen demand for paper that can be printed on to provide images of exceptionally high quality, particularly with respect to brightness, clarity, opacity, water-fastness, water resistance, bleed resistance and rub resistance. The customer further demands that paper be amenable to use with a variety of printing techniques, including not only conventional printing techniques, but also xe2x80x9cimpact-freexe2x80x9d printing techniques such as inkjet printing (particularly colored inkjet printing), laser printing, photocopying, and the like.
In response, paper manufacturers have attempted to meet their customers"" demands for such high quality paper through a process termed xe2x80x9csizing.xe2x80x9d xe2x80x9cSizing,xe2x80x9d which encompasses both xe2x80x9cinternal sizingxe2x80x9d and xe2x80x9cexternal sizing,xe2x80x9d affects the manner in which colorants and particularly ink interact with the fibers of the paper. xe2x80x9cInternal sizingxe2x80x9d involves introduction of sizing compositions within the entire fibrous mass at the pulp stage of paper manufacturing (i.e., to the wet pulp, or more specifically, to the prepared papermaking furnish) before the stock is formed into a sheet, resulting in the distribution of the sizing composition within the entire fibrous mass that is subsequently used to produce the flat fibrous paper sheet. xe2x80x9cExternal sizingxe2x80x9d (also referred to as surface application, pasting, saturating or coating) involves application of a sizing composition to at least one surface of a fibrous paper sheet, so that the composition is present on or in at least one of the two faces of the fibrous sheet. Various materials have been used as sizing agents, such as conventional and modified starches, polyvinyl alcohol, cellulosic derivatives, gelatin, rosin, proteins such as casein, natural gums and synthetic polymers. Although these materials are effective to various degrees under certain conditions, use of each is associated with certain limitations. For example, it is often necessary to use large amounts of these conventional sizing agents in order to provide paper having the desired properties. However, the opacity and brightness of the paper substrate decrease in direct proportion to the amount of sizing agent applied to the paper. Moreover, as the amount of sizing agent and/or the cost of the sizing agent increases, the cost of producing the paper increases, making high quality papers prohibitively expensive. Certain sizing agents impart relatively poor bleed resistance and water resistance of imprinted inks, and thus must be used with insolubilizing agents to ensure production of a printed paper having satisfactory water resistance.
Use of conventional sizing agents also results in a decrease in the porosity of the final paper substrate; thus, while the sized paper substrate may have the desired brightness and opacity, it may not provide for a printed image having a suitable optical density or color intensity. In addition, as the porosity of the paper increases, the paper becomes less amenable to various handling processes during manufacturing. For example, envelope manufacturers demand that the paper available to them have a relatively low porosity. If the porosity of the paper is too high, the paper is too stiff for handling by automated industrial devices for folding and sorting (e.g., devices of the xe2x80x9csuction extractorxe2x80x9d type) during envelope production. In contrast to lower porosity papers, high porosity papers also require slower machine speeds, and further require refining and draining operations that have relatively high energy costs.
Coatings have additionally been used to enhance the quality of printed images on paper, albeit with limited success. Regarding other types of substrates, a variety of coating methods and compositions have also been suggested. However, as with textiles and paper, there is not at this time any satisfactory method for improving the quality of images printed on polymeric films, metallic sheets, or the like using water-based inks.
The present invention is directed to the aforementioned need in the art, and provides an efficient, versatile and cost-effective means for treating substrates that can then be printed on to yield high quality, water-resistant printed images. The compositions and methods of the invention are amenable for use with a wide variety of substrate types, and are compatible with conventional manufacturing and post-manufacturing handling processes.
The present invention features novel image-enhancing compositions for treating a substrate to enhance the quality of images printed thereon, wherein the image-enhancing compositions are composed of an image-enhancing agent selected from one of (a) an azetidinium polymer, (b) a guanidine polymer, (c) a mixture of an azetidinium polymer and a guanidine polymer, and (d) a copolymer of an azetidinium monomer and a guanidine monomer. Substrates can be treated before or during manufacture. Substrates treated with the present image-enhancing compositions can be printed on to yield high quality printed images, particularly when printed on with an ink containing a reactive dye having ionizable and/or nucleophilic groups capable of reacting with the image-enhancing agent. The printed images are bleed-resistant, rub-resistant, water-resistant (e.g., water-fast), and/or are characterized by an enhanced chroma and hue.
It is a primary object of the invention to address the above-mentioned need in the art by providing such an image-enhancing composition that efficiently binds colorant upon printing.
Another object of the invention is to provide a treated substrate that can be printed on to yield an image that is high quality (particularly with respect to optical density and brightness), and that is bleed-resistant, rub-resistant, and water-resistant (e.g., water-fast).
Still another object of the invention is provide a method for treating substrates using the image-enhancing compositions of the invention.
Still an additional object of the invention is to provide a method for printing on a substrate to provide water-resistant (e.g., water-fast) printed images thereon.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention.